This invention relates to a dual-circuit pressure regulator with a cylindrical main housing, a first inlet chamber and a first outlet chamber connected therewith in the one end area of the main housing, with a second inlet chamber and a second outlet chamber connected therewith in the other end area of the main housing. A first pressure regulating valve is inserted between the first inlet chamber and the first outlet chamber and loaded with a control force in the opening direction by means of a spring, and a second pressure regulating valve is inserted between the second inlet chamber and the second outlet chamber which is horizontally opposed to the first pressure regulating valve and likewise loaded with a control force in the opening direction by means of a spring. Each of the first and second inlet chambers are connected with a source of pressure, in particular a different pressure circuit of a tandem master cylinder of an automotive vehicle and each of the first and second outlet chambers are connected with a pressure-consuming device, in particular a different one of the wheel brake cylinders of the rear axle of the automotive vehicle. Each of the first and second pressure regulating valves will close on attainment of a control pressure in the associated one of the inlet and outlet chambers which is predetermined by the control force and, with the pressure in the inlet chambers continuing to increase, will influence the pressure in the outlet chambers in accordance with a predetermined control behavior.
Dual-circuit pressure regulators of the aforementioned type are mainly used for automotive vehicles and serve to regulate the braking force of individual wheels. Since during braking it is particularly the rear wheels that tend to lock easily, their brake force must be reduced or limited relative to the braking force of the front wheels. For this purpose, the wheel brake cylinders of the rear wheels are connected to the outlet chambers of the dual-circuit pressure regulator, the inlet chambers of the dual-circuit pressure regulator are connected to the master brake cylinder which in turn is also connected to the wheel brake cylinders of the front wheels.
From British Pat. No. 1,253,507, published Nov. 17, 1971, a single-circuit pressure regulator is known wherein the control force of a spring for the pressure regulating valve can be set to various values in assembly. For this purpose, the abutment of the spring is shifted in the regulator housing by a suitably large amount and then secured in position.
From the U.S. Pat. No. 3,970,347, issued July 20, 1976, a dual-circuit pressure regulator is known which operates as a pressure reducer. In this known dual-circuit pressure regulator, each of the two pressure regulating valves possesses a separate spring of its own exerting a control force on the associated pressure regulating valve in the opening direction. Considering, however, that springs have manufacturing tolerances, it is not easy to set the same control force for both pressure regulating valves. Unequal control forces however, result in unequal control pressures. If in a vehicle a dual-circuit brake system with diagonally split brake circuits is provided, i.e., the right-hand front wheel and the left-hand rear wheel form one brake circuit, while the left-hand front wheel and the right-hand rear wheel form the other brake circuit different brake forces will act on the rear wheels.
Moreover, in this known dual-circuit pressure regulator, the control forces can be only changed by the use of springs of different strengths. If dual-circuit pressure regulators with different control forces are to be provided for different types of vehicle, the springs employed must be suitably different, too.